The effects of delayed reinforcement on variability and repetition of response sequences

Four experiments examined the effects of delays to reinforcement on key peck sequences of pigeons maintained under multiple schedules of contingencies that produced variable or repetitive behavior. In Experiments 1, 2, and 4, in the repeat component only the sequence right-right-left-left earned food, and in the vary component four-response sequences different from the previous 10 earned food. Experiments 1 and 2 examined the effects of nonresetting and resetting delays to reinforcement, respectively. In Experiment 3, in the repeat component sequences had to be the same as one of the previous three, whereas in the vary component sequences had to be different from each of the previous three for food. Experiment 4 compared postreinforcer delays to prereinforcement delays. With immediate reinforcement sequences occurred at a similar rate in the two components, but were less variable in the repeat component. Delays to reinforcement decreased the rate of sequences similarly in both components, but affected variability differently. Variability increased in the repeat component, but was unaffected in the vary component. These effects occurred regardless of the manner in which the delay to reinforcement was programmed or the contingency used to generate repetitive behavior. Furthermore, the effects were unique to prereinforcement delays.     

Resistance to change of responding maintained by unsignaled delays to reinforcement: a response-bout analysis

Previous experiments have shown that unsignaled delayed reinforcement decreases response rates and resistance to change. However, the effects of different delays to reinforcement on underlying response structure have not been investigated in conjunction with tests of resistance to change. In the present experiment, pigeons responded on a three-component multiple variable-interval schedule for food presented immediately, following brief (0.5 s), or following long (3 s) unsignaled delays of reinforcement. Baseline response rates were lowest in the component with the longest delay; they were about equal with immediate and briefly delayed reinforcers. Resistance to disruption by presession feeding, response-independent food during the intercomponent interval, and extinction was slightly but consistently lower as delays increased. Because log survivor functions of interresponse times (IRTs) deviated from simple modes of bout initiations and within-bout responding, an IRT-cutoff method was used to examine underlying response structure. These analyses suggested that baseline rates of initiating bouts of responding decreased as scheduled delays increased, and within-bout response rates tended to be lower in the component with immediate reinforcers. The number of responses per bout was not reliably affected by reinforcer delay, but tended to be highest with brief delays when total response rates were higher in that component. Consistent with previous findings, resistance to change of overall response rate was highly correlated with resistance to change of bout-initiation rates but not with within-bout responding. These results suggest that unsignaled delays to reinforcement affect resistance to change through changes in the probability of initiating a response bout rather than through changes in the underlying response structure.     

Reconstructing Distances among Objects from Their Discriminability

We describe a principled way of imposing a metric representing dissimilarities on any discrete set of stimuli (symbols, handwritings, consumer products, X-ray films, etc.), given the probabilities with which they are discriminated from each other by a perceiving system, such as an organism, person, group of experts, neuronal structure, technical device, or even an abstract computational algorithm. In this procedure one does not have to assume that discrimination probabilities are monotonically related to distances, or that the distances belong to a predefined class of metrics, such as Minkowski. Discrimination probabilities do not have to be symmetric, the probability of discriminating an object from itself need not be a constant, and discrimination probabilities are allowed to be 0’s and 1’s. The only requirement that has to be satisfied is Regular Minimality, a principle we consider the defining property of discrimination: for ordered stimulus pairs (a,b), b is least frequently discriminated from a if and only if a is least frequently discriminated from b. Regular Minimality generalizes one of the weak consequences of the assumption that discrimination probabilities are monotonically related to distances: the probability of discriminating a from a should be less than that of discriminating a from any other object. This special form of Regular Minimality also underlies such traditional analyses of discrimination probabilities as Multidimensional Scaling and Cluster Analysis. This research was supported by the NSF grant SES 0318010 (E.D.), Humboldt Research Award (E.D.), Humboldt Foundation grant DEU/1038348 (H.C. & E.D.), and DFG grant Co 94/5 (H.C.).     

Effects of exemplar training in exclusion responding on auditory-visual discrimination tasks with children with autism

In Experiment 1 with 7 autistic children (3 to 6 years old), auditory-visual exclusion was tested with four unknown word-item pairs for each child. One child demonstrated exclusion and positive learning outcomes unequivocally with the four auditory-visual relations. Three children demonstrated exclusion, though inconsistently, and failed to demonstrate positive learning outcomes. The remaining 3 children failed to demonstrate exclusion; therefore, the learning outcome test was omitted. The 6 children who failed to demonstrate exclusion or positive learning outcomes participated in the second experiment. In Experiment 2, nonreinforced exclusion trials with four new unknown word-item pairs were included in trial blocks that also contained reinforced exclusion trials with the unknown exemplars from Experiment 1. Five children demonstrated exclusion with the new word-item pairs, and 4 of these demonstrated positive learning outcomes in further tests. One child demonstrated some limited but inconsistent improvement in exclusion and was not tested for learning outcomes. The data suggest that contemporaneous presentation of multiple examples of reinforced exclusion facilitated nonreinforced exclusion performances and that the resulting reduction in errors was critical in producing accurate learning outcomes with the new word-item discriminations.     

Stimulus control of cocaine self-administration

Environmental stimuli that set the occasion wherein drugs are acquired can "trigger" drug-related behavior. Investigating the stimulus control of drug self-administration in laboratory animals should help us better understand this aspect of human drug abuse. Stimulus control of cocaine self-administration was generated here for the first time using multiple and chained schedules with short, frequently-alternating components--like those typically used to study food-maintained responding. The procedures and results are presented along with case histories to illustrate the strategies used to produce this stimulus control. All these multicomponent schedules contained variable-interval (VI) components as well as differential-reinforcement-of-other-behavior (DRO) or extinction components. Schedule parameters and unit dose were adjusted for each rat to produce stable, moderate rates in VI components, with minimal postreinforcement (infusion) pausing, and response cessation in extinction and DRO components. Whole-body drug levels on terminal baselines calculated retrospectively revealed that all rats maintained fairly stable drug levels (mean, 2.3 to 3.4 mg/kg) and molar rates of intake (approximately 6.0 mg/kg/hr). Within this range, no relation between local VI response rates and drug level was found. The stimulus control revealed in cumulative records was indistinguishable from that achieved with food under these schedules, suggesting that common mechanisms may underlie the control of cocaine- and food-maintained behavior.     

On the form of the forgetting function: the effects of arithmetic and logarithmic distributions of delays

Forgetting functions with 18 delay intervals were generated for delayed matching-to-sample performance in pigeons. Delay interval variation was achieved by arranging five different sets of five delays across daily sessions. In different conditions, the delays were distributed in arithmetic or logarithmic series. There was no convincing evidence for different effects on discriminability of the distributions of different delays. The mean data were better fitted by some mathematical functions than by others, but the best-fitting functions depended on the distribution of delays. In further conditions with a fixed set of five delays, discriminability was higher with a logarithmic distribution of delays than with an arithmetic distribution. This result is consistent with the treatment of the forgetting function in terms of generalization decrement.     

越老越风险规避吗？——年龄对冲动性预测决策行为的调节效应

年老化伴随着风险承担倾向的改变,而决策行为受冲动性的影响是否受到年龄的调节尚不清楚。研究采用两种不同类型的决策任务以及Barratt冲动性量表,考察老年人风险承担在自我报告和决策行为上的改变。结果显示老年人在剑桥博弈任务中更加风险寻求而在模拟充气球任务中更加风险规避。同时冲动性可以显著预测模拟充气球的行为,且该预测受到年龄的调节。研究结果提示,老年人并不是单一的更加风险规避或者风险寻求,而是与任务特异性相关。同时,冲动性可以较好的预测年轻人的决策行为,而对老年人的决策行为没有预测作用。     

An enriched teaching program for reducing resistance and indices of unhappiness among individuals with profound multiple disabilities

We evaluated an enriched teaching program for reducing resistance and indices of unhappiness displayed by 3 individuals with profound multiple disabilities during teaching sessions. The program involved presentation of preferred activities before, during, and after each teaching session, discontinuation of identified nonpreferred activities, and a brief break and preferred activity following occurrence of resistance. Implementation of the enriched teaching program was accompanied by reductions in resistance and indices of unhappiness for each participant. Results also indicated no negative impact of the program on participant performance of the teaching steps or staff teaching proficiency. Staff questionnaire responses provided a degree of social validation for the observed changes in that staff reported the participants liked the enriched teaching program more than the traditional teaching process. Directions for future research discussed include identifying critical aspects of the overall program and the potential relation between teaching proficiency and the program's enrichment effectiveness.     

Objects are individuals but stuff doesn't count: perceived rigidity and cohesiveness influence infants' representations of small groups of discrete entities

Young infants construct models of the world composed of objects tracked through time and occlusion. To date little is known about the degree to which these models are sensitive to the material make-up of the represented individuals. Two experiments probed 8-month-olds' ability to represent different kinds of entities: rigid, cohesive objects, flexible, cohesive objects, and non-rigid, non-cohesive portions of sand. In Experiment 1, infants represented an array of two rigid, cohesive objects hidden behind a single screen, but failed to represent hidden arrays of two flexible objects or two portions of sand. In Experiment 2, entities were hidden behind two screens instead of one, thereby reducing the information processing demands of the task. In that case, infants succeeded in representing arrays of both types of object stimuli, but again failed to represent the portions of sand. It is argued that (1) the processes by which infants individuate and track entities are sensitive to material kind, (2) rigid cohesive objects occupy a privileged status in this system, and (3) early knowledge about objects and substances has a quantificational aspect.